The invention concerns an arrangement for controlling a device for changing the timing of gas exchange valves of an internal combustion engine, and more particularly for controlling a hydraulic pressure cylinder having a piston which is movable between two end settings for relative rotation of a drive part of the pressure cylinder which is connected to the crankshaft in relation to a drive part of the pressure cylinder which is connected to the camshaft by controlling the hydraulic pressure in the chambers formed in the hydraulic pressure cylinder on each side of the piston.
A similar type of arrangement is previously known from DE-OS 195 05 741. With this arrangement, in order to avoid starting noises with camshaft setting mechanism, the setting mechanism basically consists of a hydraulic pressure cylinder with a piston movable between two end positions whose linear position movements are transformed into relative rotations of a drive part of the pressure cylinder connected with a crankshaft in relation to an output part of the pressure cylinder connected with a camshaft. In this arrangement, the pressure cylinder is subdivided by the piston into two pressure chambers, each having a pressure medium connection, with a hydraulic pump driven by the crank shaft being connected upstream, and a pressure medium reservoir being connected downstream. The inflow and outflow of pressure medium to the pressure chambers and accordingly the piston position required in any given case for the relative rotation between camshaft and crankshaft is controlled by a hydraulic valve arrangement governed by a motor controller which in the specific case is formed by a 4/3 way valve. This 4/3 way valve is installed at the upstream and downstream connections from both pressure chambers such that, in a first switch setting in which the one pressure chamber is connected with the pressure medium reservoir through its pressure medium connection and the other is connected with the hydraulic pump through its pressure medium connection, the piston is moved in the direction of one of its end positions. In a second switch setting of the 4/3 way valve, in which the pressure medium inflow as well as the pressure medium outflow from both chambers is blocked, any desired controlled position of the piston can be set. In a third switch setting of the 4/3 way valve in which the one pressure chamber is connected with the hydraulic pump by its pressure medium connection and the other pressure chamber is connected with the pressure medium reservoir through its pressure medium outflow, movement of the piston takes place in the direction of the other of its end positions.
The proportional valves used in practice for continuous camshaft setting mechanisms constructed as 4/3 way valves have nonetheless turned out to be relatively expensive, since they are outfitted with four control or throttle cross sections whose relationship to one another is established by the shape of the movable spool valve and the housing. Moreover, the position of all four control edges has very narrow tolerance in relation to one another, owing to which very high standards are placed on their manufacturing precision, resulting in high manufacturing costs as well. Above and beyond this, such proportional valves on principle have the disadvantage that they require a magnet with relatively large dimensions to generate a linear characteristic curve between current and the magnetic force of their magnet, or to generate a constant magnetic force at constant current over the stroke in the operating range of the magnet (which must be designed for the maximum required drive force attainable), and consequently requires a relatively large space.